1. Field of the Invention
The present invention relates generally to guide wire/sensor assemblies, wherein there are at least two electrical leads or conductors required for energizing the sensor and for signal transmission, said leads extending along the length of the guide wire between a proximal end and a distal end. In particular it relates to a coaxial, electrically conductive guide wire provided with an electrical sensor.
2. Description of the Related Art
For medical purposes many devices and applications have been disclosed and patented, wherein a miniaturized sensor is positioned in the distal region of a guide wire or a catheter. Such sensors can have various purposes, such as the measurement of pressure, temperature, flow, or for the detection of some property in vivo in a living body, e.g., pH, O2, CO2, etc.
For most applications it is required that the sensors be energized electrically, and the response be transmitted back to the exterior of the patient via electrical signals. Some applications use optical sensor devices having fiber optic signal transmission, but these fall outside the scope of the present invention.
Thus, some means of signal and energy transmission is required, and most commonly extremely thin electrical leads are provided inside the guide wire, which itself is provided in the form of a tube (of the order of 0.35 mm in outer diameter), oftentimes made of steel. In order to increase the bending strength of the tubular guide wire, a core wire is positioned inside the tube. The mentioned electrical leads are positioned in the space between the inner lumen wall and the core wire.
This design has certain drawbacks. First, it renders the assembly non-rotationally symmetric, since it is virtually impossible to distribute the electrical leads uniformly over the circumference of the core wire inside the space between the inner lumen wall and the core wire. An asymmetric configuration of leads gives rise to different bending properties in different directions of bending.
Second, there is a risk that the extremely thin leads (although coated with an insulating layer) will become damaged due to friction forces appearing in the lumen, in particular at junctions in the proximal and distal regions, where the core wire changes dimension, and where manipulations during manufacture (e.g. soldering) can cause damage to the coating and possibly cause a short-circuit.
Third, it is relatively complicated to assemble the device because of the extremely small dimensions of tubes, leads and sensors. And, fourth, electrical contacts at the proximal end of the guide wire are made using discrete components, thereby complicating the assembly.
A guide wire disclosed in EP 0 925 803, assigned to the same assignee as the present invention, attempts to solve the symmetry problem by providing electrical leads in the form of concentric layers of conducting material with insulation provide between layers. Although representing an improvement, this device also has certain drawbacks. For example, there is a risk that the concentric layers may break and cause a short-circuit. Another possible problem could be “pinholes” in the very thin insulating layers, representing a potential risk for short-circuiting.